1. Field of the Invention
The present invention generally relates to electron beam (E-beam) lithography and particularly to a methodology which compensates for repeatable across chip and across wafer line width variations in the E-beam patterned substrates (e.g., mask or wafer) from both known and unknown sources.
2. Background Description
Electron beam lithography can be viewed as a process of electronically forming precise copies of a pattern design in a resist covered substrate. It is imperative in this process that the shapes making up the pattern design be accurately placed relative to each other during the resist patterning. Equally important is the uniformity of the scaling of the shapes generated in the resist from the pattern design. In E-beam lithography, shapes imaged in the resist may exhibit systematic deviations from the designed size as a function of location on the substrate. For example, a systematic change of beam current during patterning caused by column charging can result in systematic deviations from the designed size. In addition, there may be process induced size variations that result in systematic deviations. One example of this sort of problem is the case where the image size exhibits a bowing character across a substrate. For example, the images may be 5% smaller than the nominal design at the left and right edges of the substrate and 5% larger in the center.
Often, the root cause or causes of the image size variation problem will not be known and will not be easily identified. In applications where dimensions are critical, such as integrated circuit applications having micron and submicron line widths, patterning of the substrates may need to be halted until the root causes are identified and corrected. This can lead to serious economic cost increases. What is needed is a methodology and apparatus which allows compensating for pattern deviations which have a repeatable component present, thereby allowing production to continue with or without having full knowledge of the problem's source.